1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and a structure of a semiconductor device, in particular, to a method of manufacturing a semiconductor device comprising the step of filling in a metal wire within a contact hole according to a CMP (chemical mechanical polishing) method.
2. Description of the Background Art
FIGS. 19 and 20 are cross section views showing a conventional method for manufacturing a semiconductor device in order of process steps. In reference to FIG. 19, first, a semiconductor element such as an MOSFET is formed in a silicon substrate 1 according to a well-known method and, after that, a silicon oxide film 2 as an interlayer insulating film is formed on the silicon substrate 1. Next, a contact hole 3 which functions as a hole for electrical connection between a wire and a substrate and a recess 4 which functions as an alignment mark are formed in the silicon oxide film 2 according to anisotropic dry etching method. Through the creation of the contact hole 3, a part of the source and drain regions of the MOSFET is exposed while through the creation of the recess 4, a part of the top surface of the silicon substrate 1 is exposed. The width of the recess 4 is significantly broader than the width of the contact hole 3.
Next, a titanium nitride film 5 as a barrier metal is formed on the entire surface according to a spattering method, or the like. Next, a tungsten film 106 as a conductive plug with the film thickness of approximately 400 nm is formed on the entire surface so as to fill in the contact hole 3 according to a CVD method, or the like. Concretely, the temperature is set at approximately 470xc2x0 C. for the reaction and, first, 25 sccm of WF6, 10 sccm of SiH4 and 800 sccm of H2 are used as a reactive gas in the atmosphere of 30 Torr of Ar, N2 so as to layer a seed layer with a film thickness of approximately 100 nm. After that, 75 sccm of WF6 and 500 sccm of H2 are used as a reactive gas in the atmosphere of 80 Torr of Ar, N2 so as to layer a film with a thickness of approximately 300 nm.
In reference to FIG. 20, next, the tungsten film 106 and the titanium nitride film 5 are removed through polishing until the top surface of the silicon oxide film 2 is exposed by means of a CMP method. At this time, the contact hole 3 is completely filled in with the tungsten film 106 while the recess 4 having a broad width is not completely filled in with the tungsten film 106 and, therefore, an indentation 7 is created within the recess 4 as shown in FIG. 20. After that, as the final process of the CMP step, the wafer is cleaned.
In the above described conventional method of manufacturing a semiconductor device, however, the following problem arises. FIG. 21 is a cross section view showing a partially enlarged view of the structure shown in FIG. 20. Concretely, the titanium nitride film 5 and the tungsten film 106 formed within the recess 4 are shown partially enlarged. The tungsten film 106 has grains 106a in a pillar form with a diameter of approximately 70 nm.
Though a portion of the abrasive material accumulates within the indentation 7 through the CMP process, most of it can be removed through cleaning after polishing. However, as shown in FIG. 21, since the diameter of the grains 106a is comparatively large, the unevenness of the surface of the tungsten film 6 is comparatively large. Therefore, a portion of the abrasive material 50 which has accumulated in gaps between the grains 106a cannot be adequately removed through cleaning and becomes attached to the grains 106a as foreign matter. As a result, according to a conventional method of manufacturing a semiconductor device, a problem arises that the abrasive material 50 which has attached to the grains 106a again becomes attached to the surface of the wafer in the subsequent step so as to cause a wire pattern defect or a short circuit between the wires.
According to the first aspect of the present invention, a method of manufacturing a semiconductor device comprises the steps of: (a) preparing a substrate; (b) forming a first film on the substrate; (c) forming a recess by partially hollowing a top surface of the first film in the direction toward the substrate; (d) forming a second film on a structure gained in step (c) with a film thickness such that the recess is not completely filled in; and (e) removing through polishing the second film in a part which is located above the top surface of the first film, wherein a fine grain layer, which has grains of which the diameter is small to the degree that the abrasive material used for polishing in step (e) does not easily become caught in the gaps between the grains, is formed on, at least, a top surface of the second film.
In addition, according to the second aspect of the present invention, a method of manufacturing a semiconductor device is a method of manufacturing a semiconductor device according to the first aspect, wherein the second film where the diameter of the grains in the fine grain layer is approximately 10 nm to 20 nm is formed in step (d).
In addition, according to the third aspect of the present invention, a method of manufacturing a semiconductor device is a method of manufacturing a semiconductor device according to the first or the second aspect, wherein the second film comprising the fine grain layer throughout all the film thickness is formed in step (d).
In addition, according to the fourth aspect of the present invention, a method of manufacturing a semiconductor device is a method of manufacturing a semiconductor device according to the first or the second aspect, wherein the second film having the fine grain layer in only the top surface is formed in step (d).
In addition, according to the fifth aspect of the present invention, a method of manufacturing a semiconductor device comprises the steps of: (a) preparing a substrate; (b) forming a first film on the substrate; (c) forming a first recess by partially hollowing a top surface of the first film in the direction toward the substrate; (d) forming a second film on a structure obtained in step (c) with a film thickness such that the recess is not completely filled in; (e) removing a top surface of the second film by means of isotropic etching; and (f) after step (e), removing through polishing a part of the second film which is located above the top surface of the first film.
In addition, according to the sixth aspect of the present invention, a method of manufacturing a semiconductor device comprises the steps of: (a) preparing a substrate; (b) forming a first film on the substrate; (c) forming a recess by partially hollowing a top surface of the first film in the direction toward the substrate; (d) forming a second film on a structure obtained in step (c) with a film thickness such that the recess is not completely filled in; (e) forming a third film in a thin film form on the second film; (f) removing through polishing a parts of the second and third films which are located above the top surface of the first film; and (g) after step (f), removing the third film which remains in the recess.
In addition, according to the seventh aspect of the present invention, a method of manufacturing a semiconductor device comprises the steps of: (a) preparing a substrate; (b) forming a first film on the substrate; (c) forming a first recess by partially hollowing a top surface of the first film in the direction toward the substrate; (d) forming a second film on a structure obtained in step (c) with a film thickness such that the first recess is not completely filled in; (e) forming a third film with a film thickness such that the level of a top surface thereof agrees with, or is higher than, the level of the top surface of the first film in a second recess which is defined by a top surface of a part of the second film which is formed in the first recess; (f) removing through polishing a part of the second film which is located above the top surface of the first film; and (g) after step (f), removing the third film which remains in the second recess.
In addition, a method of manufacturing a semiconductor device according to the eighth aspect of the present invention is a method of manufacturing a semiconductor device according to the sixth or the seventh aspect, wherein, in step (g) the third film is removed through wet etching and the etching rate of the third film in the etching solution used for the wet etching is significantly greater than the etching rate of the first film in the etching solution.
In addition, according to the ninth aspect of the present invention, a semiconductor device comprises: a substrate; a first film formed on the substrate; a recess partially formed in a top surface of the first film; and a second film formed on the sides and the bottom of the recess with a film thickness such that the recess is not completely filled in, wherein the semiconductor device is characterized in that a fine grain layer of which the diameter of the grains is approximately 10 nm to 20 nm is formed on, at least, the top surface of the second film.
According to the first aspect of the present invention, a variety of problematic conditions due to abrasive material becoming attached to the grains that later becomes again attached to the surface of the wafer in subsequent steps such as the occurrence of wire pattern defects or short circuits between wires can be prevented.
In addition, according to the second aspect of the present invention, since the diameter of the grains is sufficiently small, the amount of the abrasive material which becomes attached to the grains can be effectively reduced.
In addition, according to the third aspect of the present invention, since only one type of material may be used for the second film, the number of manufacturing steps can be reduced in comparison with the case where a plurality of types of materials are used.
In addition, according to the fourth aspect of the present invention, since a material which is excellent for covering steps can be used on the parts other than the top surface of the second film, the degree of filling in within the recess of the second film can be increased.
In addition, according to the fifth aspect of the present invention, the grains on the top surface of the second film can be changed from a rugged, uneven condition to a smooth, rounded condition by means of isotropic etching in step (e). Thereby, the abrasive material can be prevented from becoming attached to the grains.
In addition, according to the sixth aspect of the present invention, the abrasive material accumulates on the third film in a thin film form is step (f). Then, the third film is removed in the subsequent step (g) and, at that time, the abrasive material is also removed so that the abrasive material can be prevented from remaining within the recess.
In addition, according to the seventh aspect of the present invention, after the third film is formed within the second recess in step (e), polishing of the second film is carried out in step (f). Accordingly, the abrasive material can be prevented from remaining within the second recess.
In addition, according to the eighth aspect of the present invention, at the time when the third film is removed in step (g) the removal of the first film, at the same time, can be avoided.
In addition, according to the ninth aspect of the present invention, foreign matter attached to the grains can be prevented from becoming again attached to the wafer surface in subsequent steps of a manufacturing process for a semiconductor device. Therefore, a semiconductor device with a high reliability can be gained.
The present invention is provided to solve these problems and has a purpose of providing a method of manufacturing a semiconductor device which can reduce or prevent abrasive material from remaining within an indentation in the surface after a CMP process.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.